Ubuntu all screwy after dist-upgrade. Can't bring up grub screen either

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http://askubuntu.com – OK, so after last night's dist upgrade, I'm getting the following symptoms: After restarting computer several times. One of my screens (always the same one) is split down the middle. Not always in the same place, and sometimes shows "trails". This is not a hardware problem: during boot both screens work fine. I'ts only once the Ubuntu log-in screen shows up that the screen goes screwy. Unity desktop half-loads and then doesn't respond to any command. The mouse moves but nothing is clickable. Xmonad desktop responds (I'm on Xmonad desktop right now, using the second screen). Curiously: (HowTos)